Prior to the conception and development of the present invention, railway car hand brake mechanisms were generally well known in the art. They usually include a large, rotatable hand wheel disposed in a vertical plane and mounted on a shaft which, through a gear train, can rotate a chain drum to wind up a chain that is secured at its end remote from the chain drum to the brake rigging of the railway car. As the hand wheel is rotated in one direction, the brakes are applied and rotation of the hand wheel shaft in the opposite direction is prevented by a pawl which engages a detent wheel on the hand wheel shaft.
These hand brake mechanisms further provide a clutch mechanism for facilitating a gradual release of the brake. When a hand wheel is rotated clockwise (as viewed from the front of the unit), such rotation is transmitted directly through a drive shaft, a pinion, a gear, and a winding drum to take up slack of a chain connected to the brake rigging. When resistance is offered by the chain to further rotation of the hand wheel, such resistance, acting back through the drum, the gear, and pinion, causes a nut to be advanced on a threaded portion of the drive shaft to move against a ratchet member which is clamped between respective friction surfaces on the nut and on the drive shaft, thus causing the drive shaft, ratchet, and the nut to rotate as a unit. A pawl prevents rotation of the ratchet in the opposite direction. The hand wheel torque is increased until a state of static equilibrium is reached, or at the point at which the brakes are fully applied, whereupon rotation of the hand wheel is terminated, and the clamped ratchet, by means of the holding pawl, prevents the chain from unwinding.
The clutch mechanism also provides for quick release of the brakes by operating a release handle which effects disengagement of the normally engaged clutch and thereby allows free rotation of the pinion and gear to release the chain load while the nut and ratchet are held stationary by the holding pawl. The brakes may be released by disengaging the pawl from the detent wheel but this causes rapid rotation of the hand wheel and the gears of the gear train. To avoid rapid rotation of the hand wheel, hand brake mechanisms have been devised which are known as “quick release” mechanisms.
U.S. Pat. No. 4,714,142 titled Railway Car Hand Brake with Release Governor teaches such a hand brake having a quick release mechanism. The quick release mechanism includes a cam mounted on a manually pivotable shaft substantially attached to a quick release handle. During quick release, rotation of the quick release lever rotates the cam which engages a crank and forces it to move downwardly and disengage the pinion from the clutch collar. With the pinion disengaged from the clutch mechanism, the holding pawl and detent gear can no longer prevent its rotation, therefore it rotates freely about the drive shaft causing quick release of the brakes without rotation of the hand wheel. Opposite movement of the quick release handle releases the clutch collar and forces the clutch collar to reengage the pinion under the force of the spring acting on such collar and allow for a normal brake application.
The teachings of the U.S. Pat. No. 4,714,142 are hereby incorporated in present application by reference thereto.
In order for the quick release mechanism to function properly, the quick release lever, rotatable approximately 30 degrees to release the brake, must be held in the released position until the entire chain has been expelled. It has been found that when a hand brake is quick released using the lever, the lever is not left in its full released position long enough to fully expel the chain from the hand brake, thus maintaining residual tension due to lack of sufficient slack. As a result the bakes may be applied unintentionally during railcar motion, especially around the curve.
As it can be seen from the above discussion, prior to the instant invention, there has been a need for a positive means for maintaining the quick release mechanism in the released hold position to avoid unintentional application of the railcar brake rigging.